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Adds automatic gain control to P25 C4FM decoder to condition the

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samples prior to interpolation.

Resolves issue with using incorrect quadrature index when pulling a
sample from the interpolating buffer.

Resolves issue where the instrumented version of the interpolating
buffer was being constructed in the non-interpolated decoder component.
This commit is contained in:
Denny
2018-04-18 05:47:17 -04:00
parent 3619b480f8
commit 95aa9f8803
2 changed files with 9 additions and 5 deletions
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2
src/main/java/io/github/dsheirer/dsp/psk/InterpolatingSampleBuffer.java
View File

@@ -130,7 +130,7 @@ public class InterpolatingSampleBuffer
*/
public Complex getPrecedingSample()
{
mPrecedingSample.setValues(mDelayLineInphase[mDelayLinePointer + 4], mDelayLineQuadrature[mDelayLinePointer + 3]);
mPrecedingSample.setValues(mDelayLineInphase[mDelayLinePointer + 3], mDelayLineQuadrature[mDelayLinePointer + 3]);
return mPrecedingSample;
}

12
src/main/java/io/github/dsheirer/module/decode/p25/P25_C4FMDecoder.java
View File

@@ -20,9 +20,9 @@ import io.github.dsheirer.dsp.filter.FilterFactory;
import io.github.dsheirer.dsp.filter.design.FilterDesignException;
import io.github.dsheirer.dsp.filter.fir.FIRFilterSpecification;
import io.github.dsheirer.dsp.filter.fir.complex.ComplexFIRFilter;
import io.github.dsheirer.dsp.gain.ComplexFeedForwardGainControl;
import io.github.dsheirer.dsp.psk.DQPSKDemodulator;
import io.github.dsheirer.dsp.psk.InterpolatingSampleBuffer;
import io.github.dsheirer.dsp.psk.InterpolatingSampleBufferInstrumented;
import io.github.dsheirer.dsp.psk.pll.CostasLoop;
import io.github.dsheirer.sample.Listener;
import io.github.dsheirer.sample.complex.ComplexBuffer;
@@ -38,6 +38,7 @@ import java.util.concurrent.ScheduledExecutorService;
public class P25_C4FMDecoder extends P25Decoder implements IComplexBufferListener, Listener<ComplexBuffer>
{
private final static Logger mLog = LoggerFactory.getLogger(P25_C4FMDecoder.class);
private ComplexFeedForwardGainControl mAGC = new ComplexFeedForwardGainControl(32);
protected static final double SYMBOL_RATE = 4800;
protected InterpolatingSampleBuffer mInterpolatingSampleBuffer;
protected DQPSKDemodulator mQPSKDemodulator;
@@ -65,7 +66,7 @@ public class P25_C4FMDecoder extends P25Decoder implements IComplexBufferListene
mCostasLoop = new CostasLoop(mSampleRate, SYMBOL_RATE);
mInterpolatingSampleBuffer = new InterpolatingSampleBufferInstrumented((float)(sampleRate / SYMBOL_RATE));
mInterpolatingSampleBuffer = new InterpolatingSampleBuffer((float)(sampleRate / SYMBOL_RATE));
mQPSKDemodulator = new DQPSKDemodulator(mCostasLoop, mInterpolatingSampleBuffer);
//Message framer can trigger a symbol-inversion correction to the PLL when detected
@@ -77,8 +78,11 @@ public class P25_C4FMDecoder extends P25Decoder implements IComplexBufferListene
@Override
public void receive(ComplexBuffer complexBuffer)
{
ComplexBuffer filtered = filter(complexBuffer);
mQPSKDemodulator.receive(filtered);
ComplexBuffer basebandFiltered = filter(complexBuffer);
ComplexBuffer gainApplied = mAGC.filter(basebandFiltered);
mQPSKDemodulator.receive(gainApplied);
}
protected ComplexBuffer filter(ComplexBuffer complexBuffer)